In electronic circuits, voltage regulators provide substantially constant supply voltages for voltage sensitive portions of the circuit. Usually, regulators have a pass transistor to change a preferably low voltage drop between input and output, a voltage sensor at the output and a feedback unit which controls the pass transistor. The output voltage (e.g., constant 5 volts) should be independent of temperature, so that a temperature compensation circuit is sometimes required.
U.S. Pat. No. 5,686,821 to Brokaw [1] teaches a regulator with a two-resistor voltage sensor carrying a current proportional to the absolute temperature (PTAT). The resistors (R9 and R10 in FIG. 4 of [1]) have a value ratio related to a voltage provided by a bandgap reference. Positive and negative temperature coefficients of the current and the bandgap voltage compensate each other. A further useful reference is: Horowitz, P., Hill, W.: "The art of electronics", Second Edition, Cambridge University Press, chapter 6.15: "Bandgap (V.sub.BE) reference", on pages 335-341 [2].
The output voltage should also have low noise components. Also, the feedback unit should not cause the regulator to oscillate. Regulators can have so-called bypass capacitors which function as noise filters and pole suppression filters. But, the bypass capacitor increases the turn-on time of the regulator. Capacitors are also not wanted because of their physical size.
The present invention seeks to provide regulators which mitigate or avoid these and other disadvantages and limitations of the prior art.